Synchronizer sleeve for a change speed gear and method of manufacturing same

ABSTRACT

The present invention refers to a synchronizer sleeve and a method of manufacturing a synchronizer sleeve for a change speed gear. The synchronizer sleeve comprises in a known manner a shift fork recess opening towards the outer peripheral surface and a toothing formed at its inner peripheral surface. The synchronizer sleeve according to the invention, which can be manufactured at a low price without affecting the wear to resistance, is characterized according to the invention by a surface hardness of the shift-force recess, which is set by cold rolling, wherein the toothing is hardened locally, in particular it is hardened inductively. In the method of manufacturing the synchronizer sleeve according to the invention the shift fork recess is ready worked by cold rolling.

[0001] The present invention refers to a synchronizer sleeve for a change speed gear, which comprises a shift fork recess opening towards the outer peripheral surface of the synchronizer sleeve, and a toothing formed at its inner peripheral surface.

[0002] Synchronizer sleeves of this type are used in manual change speed gears. Then the synchronizer sleeve comprises at least one pressure surface which is regularly hardened and formed at the front end side of the synchronizer sleeve and which cooperates with a synchronizing ring for the frictional synchronization of the rotational speed. If synchronizer sleeves are used in electrically shifting gears in which the synchronization is carried out electronically, the formation of such a pressure surface at the front end side of the synchronizer sleeve can be renounced.

[0003] Synchronizer sleeves are usually manufactured from a blank generated by means of shaping, preferably by forging, said blank being fully turned on the lathe to manufacture the final contour of the ready synchronizer sleeve. On the inner peripheral surface of the synchronizer sleeve, a toothing is then broached or shaped in a conventional manner. Undercuts of this toothing are usually manufactured by rolling. Then details are milled. The component manufactured in this manner is then carburized.

[0004] In a manufacturing method of this type a certain surface hardness determined by the carburizing or nitriding process results on the entire component.

[0005] The carburizing of the synchronizer sleeve on the one hand involves the disadvantage that the component finished in its final contour must run through a relatively long hardening process. Moreover, a casting at the component may occur during the carburizing process so that the dimensional accuracy of the synchronizer sleeve is affected. Due to the instrumental and timely effort, the carburizing process is relatively expensive.

[0006] The object of the present invention is to provide a synchronizer sleeve, which without affecting the resistance to wear of the component can be manufactured in a more inexpensive way. The object of the invention is furthermore to provide a method for the inexpensive manufacture of a synchronizer sleeve.

[0007] To solve this object, the synchronizer sleeve of the above-mentioned type is developed by the present invention in that the surface hardness of the shift fork recess is set by work-hardening and that the toothing is locally hardened, in particular inductively hardened.

[0008] The synchronizer sleeve according to the invention is not hardened on the whole during a hardening process, but it is hardened only locally in the area of the toothing. The shift fork recess which in the prior art is first of all turned off on the lathe and then hardened during the hardening process to protect it against wear by the sliding pad arranged in the shift fork recess, has a surface hardness set by the work hardening process, preferably by cold rolling. The shift fork recess is brought to its final contour when cold rolling the blank and is at the same time hardened. It evolved that in case of a suitable material selection for the synchronizer sleeve, the solidification of the surfaces by cold rolling in the area of the shift fork recess is sufficient to set a wear resistance of the synchronizer sleeve which is sufficient with respect to a sliding pad engaging into the shift fork recess. The surface of the shift fork recess in the synchronizer sleeve according to the invention is not additionally hardened by carburizing or nitriding. In the frictional combination shift force recess/sliding pad, the sliding pad is usually provided as the softer component, i.e. as a wear component of the frictional combination.

[0009] In the synchronizer sleeve according to the invention, the toothing is hardened locally only, preferably it is hardened inductively. Preferably an inductive hardening process is applied in frequency ranges, that are to be adapted to the respective application. An inductive hardening process by using different frequencies is also possible (multi-frequency curing). The adjustment of suitable parameters for the inductive hardening process are left to the expert's discretion and are to be adjusted in accordance with the respective material and the toothing geometry. When hardening the toothing, in particular the surface of the teeth is to be strengthened. By appropriately adapting the method parameters it is also possible to adjust the desired strength in the tooth root of the individual teeth. The local hardening of the toothing offers the possibility to only increase the hardness of the surface of the teeth and to adjust the core portion of the teeth in the desired manner. A local hardening can be controlled more precisely compared to carburization. Moreover, it requires less time. A casting of the component is less dominant by the local heat effect than is for instance the case in carburization.

[0010] A preferred development of the synchronizer sleeve according to the invention is defined in claim 2.

[0011] To solve the object with respect to the method, the priorly known method is developed in that a shift fork recess opening towards the peripheral surface of the synchronizer sleeve can be finished by cold rolling.

[0012] While in the known method the surface portion of the shift fork recess hardened by cold rolling was first of all worked in a machining manner and was then hardened in its final contour adjusted by a machining process, the finish work of the shift fork recess in the manufacturing method according to the invention is carried out by cold rolling. Further method steps are no longer required at least not at the outer peripheral surface. The toothing regularly formed at the inner peripheral surface may be formed by shrinking an annular gear A toothing at the cold-rolled component can also be formed in a directly chip-removing manner and can be subsequently locally hardened.

[0013] When manufacturing a synchronizer sleeve for a manual change speed gear, the pressure surface preferably formed at the front end side of the synchronizer sleeve is formed during the local hardening process of the toothing. The pressure surface is formed preferably directly at the inner peripheral surface of the synchronizer sleeve so that the local hardening of the toothing at the inner peripheral surface of the synchronizer sleeve also leads to an increase of the hardness in a partial section of the annular surfaces of the synchronizer sleeve. 

1. A synchronizer sleeve for a change speed gear, which comprises a shift fork recess opening towards its outer peripheral surface and a toothing formed at its inner peripheral surface, characterized in that the surface hardness of the shift fork recess is adjusted by work-hardening and that the toothing is locally hardened, in particular inductively hardened
 2. A synchronizer sleeve as claimed in claim 1 , characterized in that a pressure surface formed at the front end side of the synchronizer sleeve is formed directly adjacent to the toothing.
 3. A method of manufacturing a synchronizer sleeve for a change speed gear, in which a blank is cold-rolled, and subsequently a toothing is formed at the inner peripheral surface of the synchronizer sleeve, characterized in that a shift fork recess opening towards the peripheral surface of the synchronizer sleeve is ready manufactured by cold-rolling and is adjusted with respect to the surface hardness.
 4. A method as claimed in claim 3 , characterized in that the toothing is hardened locally.
 5. A method as claimed in claim 4 , characterized in that the toothing is hardened inductively, preferably by means of multi-frequency hardening.
 6. A method as claimed in one of claims 3 to 5 , characterized in that a front-end sided pressure surface is locally hardened together with the toothing 